As multiple-input multiple-output (MIMO) technology has developed over the years, the number of antennas in the deployed MIMO systems has been steadily increasing. The concept of using a large number (hundreds or thousands) of antennas has also been brought up from an information theory perspective. However, the challenges of implementing hundreds or thousands of antennas in conventional cellular systems have been prohibitive. For example, to accommodate 1024 half-wavelength antennas in 2G Hz band, the dimension of the antenna array will be around 2.4 m×2.4 m.
Proposals for a mobile broadband system using millimeter-wave bands (MMB) have opened up opportunities to bring large MIMO antenna arrays with hundreds or thousands of antennas. For example, using millimeter-wave frequencies around 30 GHz, the dimension of an antenna array with 1024 antennas is about 16 cm×16 cm, smaller than a single sector antenna for a typical cellular base station.
The transmitter and receiver beamforming in MMB systems are different from the MIMO operations in cellular systems. With possibly thousands of antennas at a base station and hundreds of antennas at a mobile station, the spatial degree of freedom of MMB systems is much larger than that of cellular systems. To drive hundreds or thousands of antennas, a large number of power amplifiers are needed, each having its own power constraint. The design of efficient beamforming schemes to fully utilize the power of all these power amplifiers is an interesting problem with practical significance.
Therefore, there is a need in the art for improved transmission strategies in multiple antenna wireless communication systems. In particular, there is a need for methods and apparatuses that are capable of multiple antenna transmission schemes with per-antenna power constraints.